1. Technical Field
The present invention relates to a data processor and a data processing method for storing data to be processed in a storage device, and performs an erasing process to erase the processed data stored in the storage device after the data is processed, as well as a computer readable medium storing a program therefor.
2. Related Art
In recent years, an image processor, such as a copy machine and a printer, employs a hard disk as a storage device to hold image data. However, if such an image processor is discarded together with the hard disk, there is a problem that information held within the discarded hard disk may leak out. Therefore, a need for erasing unnecessary information within the hard disk is growing, and various ways have been proposed as a method to erase the information in the hard disk.
As an example of such erasing method, it is disclosed that dummy data is prepared (overwriting data) to overwrite a memory at a preset timing such as during intervals between print jobs, and a hard disk area to be subjected to erasing is overwritten by the dummy data.
However, in a storage device that magnetically stores data, such as a hard disk, there is a possibility that overwriting only once does not completely erase the data beneath. It is because the contents of the hard disk may be restored by dismantling a HDD (hard disk drive) and reading residual magnetism on the disk by a particular kind of reader.
Therefore, there is generally known a method to erase data on a HDD, which is recommended by the US National Security Agency (NSA). In this method, overwriting three times is performed; the first and the second overwriting are performed with a random number, and the third overwriting is performed with a fixed value. There is also known an alternative method in general, which further improves the erasing effect by increasing overwriting times.
However, depending on data amount to be erased or how it is erased, it may take an enormously long time for erasing, or a long period of time may be required after a certain process is finished until a subsequent process is ready to be performed. Furthermore, since this erasing process has a certain effect on other jobs, it may cause a deterioration of performance in the entire system.